1. Buy (Apple) Lightning cable
2. Plug cable in USB-port in armrest
3. Enjoy full compatibility as with a snap-in (except for extra antenna)
4. As the cable fits through the compartment box when closed, you enjoy a lot more flexibilty with your iPhone.

I'm not sure there is an aerial line in via the Lightning connector to the iPhone 5, which would boost range either via the adapter or just the Lightning to USB. If correct, the adapter offers little benefit apart from neatness